This invention relates to a hearing aid having at least one rechargeable battery, and in particular, to a recharging system that monitors the amount of charge in the battery during charging.
Hearing aids having rechargeable batteries have been known in the art for a long time; e.g., see U.S. Pat. No. 3,297,933 (McCarthy). The trade-off between rechargeable batteries and non-rechargeable batteries is the inconvenience of having to replace the battery. There is also a trade-off in capacity. A non-rechargeable battery lasts much longer than a rechargeable battery having the same outside dimensions as the non-rechargeable battery. This is due to the different chemistries of the two types of batteries.
The inconvenience of having to remove the battery from a hearing aid initially applied both to rechargeable batteries and non-rechargeable batteries. The sole advantage of rechargeable batteries was not having to be replaced. Then, chargers were developed that made electrical contact with the hearing aid, obviating the need to remove the rechargeable battery; e.g. see U.S. Pat. No. 3,493,695 (Stork). This simplified matters for those lacking the dexterity to remove and insert a battery. Having exposed electrical contacts is undesirable and inductive chargers solved this problem; e.g. see U.S. Pat. No. 4,379,988 (Mattatall).
Inductive chargers have their own set of difficulties, including adequate coupling between the primary inductor in the charger and the secondary inductor in the hearing aid; e.g. see U.S. Pat. No. 6,658,124 (Meadows). Even with adequate coupling, rechargeable batteries are not a panacea. Most rechargeable batteries, e.g. nickel cadmium, lithium ion, and others, have “memory.” Memory in a battery relates to the amount of stored energy that it available after several discharge-charge cycles. If, for example, half the energy is used and a battery is recharged, then, eventually, only half the energy is available. Also, some rechargeable batteries do not like being overcharged, such as lithium ion batteries. These batteries overheat and rupture, sometimes violently, or catch fire. Currently, nickel-metal-hydride (NiMH) batteries are preferred for hearing aids because they have little memory and are more tolerant of overcharging.
The problems of memory and overcharging are particularly acute for hearing aids because a hearing aid may partially discharge a battery during the day and then be placed on a charger overnight. If more than one hearing aid is used, the batteries may be in different states of charge but are charged simultaneously.
It is known in the art that it is desirable to know the state of charge of a battery in a hearing aid; see Patent Application Publication US2003/0171787 (Money et al.). The published application refers to an “external controller” that “interrogates” a cochlear implant to determine the level of charge in a battery included in the implant.
It is known in the art to use a “wireless interconnection” to program hearing aids; see U.S. Pat. No. 6,888,948 (Hagen et al.). Transferring programming data to a hearing aid is disclosed. Transferring data from a hearing aid is not disclosed in the Hagen et al. patent, nor is controlling a charging cycle by communicating with a hearing aid.
In view of the foregoing, it is therefore an object of the invention to provide a rechargeable hearing aid that communicates with a charger to prevent overcharging.
Another object of the invention is to provide a battery charger and hearing aid that obviate the need for careful alignment of the hearing aid in the charger for optimum inductive coupling.
A further object of the invention is to provide a rechargeable hearing aid that can conduct two way communication with a charger.